Concentrating solar power with glasshouses

ABSTRACT

A protective transparent enclosure (such as a glasshouse or a greenhouse) encloses a concentrated solar power system. The concentrated solar power system includes one or more solar concentrators and one or more solar receivers. Thermal power is provided to an industrial process, electrical power is provided to an electrical distribution grid, or both. In some embodiments, the solar concentrators are parabolic trough concentrators with one or more lateral extensions. In some embodiments, the lateral extension is a unilateral extension of the primary parabolic trough shape. In some embodiments, the lateral extensions are movably connected to the primary portion. In some embodiments, the lateral extensions have a focal line separate from the focal line of the base portion. In some embodiments, the greenhouse is a Dutch Venlo style greenhouse.

CROSS REFERENCE TO RELATED APPLICATIONS

Priority benefit claims for this application are made in theaccompanying Application Data Sheet, Request, or Transmittal (asappropriate, if any). To the extent permitted by the type of the instantapplication, this application incorporates by reference for all purposesthe following applications, all commonly owned with the instantapplication at the time the invention was made:

-   -   U.S. Provisional Application (Docket No. 310618-2001 and Ser.        No. 61/149,292), filed Feb. 2, 2009, first named inventor Rod        MacGregor, and entitled Concentrating Solar Power with        Glasshouses;    -   U.S. Provisional Application (Docket No. CLEN-002/00US        310618-2002 and Ser. No. 61/176,041), filed May 6, 2009, first        named inventor Peter Von Behrens, and entitled Concentrating        PhotoVoltaics with Glasshouses;    -   PCT Application (Docket No. GP-09-01PCT and Serial No.        PCT/US10/22780), filed Feb. 1, 2010, first named inventor        Roderick MacGregor, and entitled Concentrating Solar Power with        Glasshouses; and    -   U.S. Provisional Application (Docket No. GP-10-02 and Ser. No.        61/361,509), filed Jul. 5, 2010, first named inventor Peter Von        Behrens, and entitled Concentrating Solar Power with        Glasshouses.

BACKGROUND

1. Field

Advancements in concentrated solar thermal power (CST), photovoltaicsolar energy (PV), concentrated photovoltaic solar energy (CPV), andindustrial use of concentrated solar thermal energy are needed toprovide improvements in performance, efficiency, and utility of use.

2. Related Art

Unless expressly identified as being publicly or well known, mentionherein of techniques and concepts, including for context, definitions,or comparison purposes, should not be construed as an admission thatsuch techniques and concepts are previously publicly known or otherwisepart of the prior art. All references cited herein (if any), includingpatents, patent applications, and publications, are hereby incorporatedby reference in their entireties, whether specifically incorporated ornot, for all purposes.

Concentrated solar power systems use mirrors, known as concentrators, togather solar energy over a large space and aim and focus the energy atreceivers that convert incoming solar energy to another form, such asheat or electricity. There are several advantages, in some usagescenarios, to concentrated systems over simpler systems that directlyuse incident solar energy. One advantage is that more concentrated solarenergy is more efficiently transformed to heat or electricity than lessconcentrated solar energy. Thermal and photovoltaic solar receiversoperate more efficiently at higher incident solar energy levels. Anotheradvantage is that non-concentrated solar energy receivers are, in someusage scenarios, more expensive than mirror systems used to concentratesunlight. Thus, by building a system with mirrors, total cost ofgathering sunlight over a given area and converting the gatheredsunlight to useful energy is reduced.

Concentrated solar energy collection systems, in some contexts, aredivided into four types based on whether the solar energy isconcentrated into a line-focus receiver or a point-focus receiver andwhether the concentrators are single monolithic reflectors or multiplereflectors arranged as a Fresnel reflector to approximate a monolithicreflector.

A line-focus receiver is a receiver with a target that is a relativelylong straight line, like a pipe. A line-focus concentrator is areflector (made up of a single smooth reflective surface, multiple fixedfacets, or multiple movable Fresnel facets) that receives sunlight overa two dimensional space and concentrates the sunlight into asignificantly smaller focal point in one dimension (width) whilereflecting the sunlight without concentration in the other dimension(length) thus creating a focal line. A line-focus concentrator with aline-focus receiver at its focal line is a basic trough system. Theconcentrator is optionally rotated in one dimension around its focalline to track daily or seasonal (apparent) movement of the sun toimprove total energy capture and conversion.

A point-focus receiver is a receiver target that is essentially a point,but in various approaches is a panel, window, spot, ball, or othertarget shape, generally more equal in width and length than a line-focusreceiver. A point-focus concentrator is a reflector (made up of a singlesmooth reflective surface, multiple fixed facets, or multiple movableFresnel facets) that receives sunlight over a two-dimensional space andconcentrates the sunlight into a significantly smaller focal point intwo dimensions (width and length). A monolithic point-focus concentratorwith a point-focus receiver at its focal point is a basic dishconcentrated solar system. The monolithic concentrator is optionallyrotated in two dimensions to rotate its focal axis around its focalpoint to track daily and seasonal movement of the sun to improve totalenergy capture and conversion.

A parabolic trough system is a line concentrating system using amonolithic reflector shaped like a large half pipe having a shapedefined by the equation y²=4fx where f is the focal length of thetrough. The reflector has a 1-dimensional curvature to focus sunlightonto a line-focus receiver or approximates such curvature throughmultiple facets fixed relative to each other.

A concentrating Fresnel reflector is a line concentrating system similarto the parabolic trough replacing the trough with a series of mirrors,each the length of a receiver, that are flat or alternatively slightlycurved in width. Each mirror is individually rotated about its long axisto aim incident sunlight onto the line-focus receiver.

A parabolic dish system is a point concentrating system using amonolithic reflector shaped like a bowl. The reflector has a2-dimensional curvature to focus sunlight onto a point-focus receiver orapproximates such curvature through multiple flat or alternativelycurved facets fixed relative to each other.

A solar power tower is a point concentrating system similar to theparabolic dish, replacing the dish with a 2-dimensional array of mirrorsthat are flat or alternatively curved. Each mirror (heliostat) isindividually rotated in two dimensions to aim incident sunlight onto apoint-focus receiver. The individual mirrors and an associated controlsystem are parts of a point-focus concentrator with a focal axis thatrotates around its focal point.

In solar thermal systems, the receiver is a light to heat transducer.The receiver absorbs solar energy, transforming it to heat andtransmitting the heat to a thermal transport medium such as water,steam, oil, or molten salt. The receiver converts solar energy to heatand minimizes and/or reduces heat loss due to thermal radiation. Inconcentrated photovoltaic systems, the receiver is a photovoltaicsurface that directly generates electricity from sunlight. In some solarthermal systems, CPV and CST are combined in a single system where athermal energy system generates thermal energy and acts as a heat sinkfor photovoltaic cells that operate more efficiently when cooled. Otherreceivers, such as a stirling engine, that use solar energy to generateheat and then locally convert the heat to electricity through mechanicalmotion and an electric generator, are also deployed as a receiver, insome approaches.

In some concentrated solar systems, such as some systems with highconcentration ratios, overall system is cost dominated by variouselements such as the concentration system (such as a mirror or lens), asupport system for the concentrators, and motors and mechanisms thatenable tracking movement of the sun. The elements dominate the costsbecause the elements are enabled to withstand wind and weather. In someusage scenarios, solar energy systems are enabled to withstand variousenvironmental dangers such as wind, rain, snow, ice, hail, dew, rodents,birds and other animals, dust, sand, moss, and other living organisms.Reflectivity of a concentrator is sensitive to damage, tarnishing, anddirt buildup since only directly reflected sunlight, not scatteredsunlight, is effectively focused.

Glass mirrors are used in some concentrated systems, because of anability to maintain good optical properties over long design lives (e.g.30 years) of concentrated solar systems. Glass is relatively fragile andvulnerable to hail and other forms of damage unless it is suitablythick, e.g. 4-5 mm for relatively larger mirrors. In a 400 square footconcentrating dish the thickness results in a weight of close to 1000lbs or about nine kg per square meter of concentrator area. The mirroris formed in a precise curve, in one dimension for a trough, in twodimensions for a dish, to focus sunlight.

In some concentrated systems, mirror surfaces cease to focus as intendedif warped. Thus, the reflector is supported and held in shape by a metalsuperstructure that is shaped to the curved glass. The superstructuresupports and protects the mirror from environmental conditions such aswinds of 75 mph or more. The protection from winds adds an additional10,000 lbs of load beyond the 1000 lb weight of the mirror, resulting incomplex construction requiring roughly 20 kg of structural steel forevery square meter of mirror area in a dish system.

In some concentrated systems, concentrator tracking motors move the 30kg per square meter weight of the concentrator, and also overcome forceof wind that exceeds an additional 300 kg per square meter. The motorsare exposed to environmental elements (such as, dirt, dust, moisture,etc).

In some concentrated systems, troughs are spaced relatively far apart on(e.g. level) ground to avoid shading each other. Avoiding shading isimportant because the trough mirror is relatively expensive and sohaving any mirror shaded (and unproductive) is costly. Few approachesexceed ground coverage of 33% since that spacing avoids shading inwinter (for an east/west orientation) or early/late in the day (for anorth/south orientation). Some east/west orientations (e.g. with 33%ground coverage), have essentially no shading of any trough surface byanother at any time during the day or year, capture almost all incidentlight within a trough array boundary during the winter (when the troughsare held vertical), but capture only about ⅓ of incident light withinthe trough array boundary during the summer (when the troughs are heldhorizontal).

Troughs are placeable with length running north/south or east/west. Ifplaced running north/south, then they are rotated during the day totrack the daily movement of the sun and keep incident light focused onthe receiver. In the morning, the trough is aimed to the east at therising sun, at noon it is aimed up at the noonday sun, and in theevening it is aimed to the west at the setting sun. North/south troughsdo not track seasonal variation in sun position. Instead, as the sunmoves lower in the sky (toward the horizon of the equator) during thewinter, light strikes the trough and reflects up the trough (away fromthe equator) to the receiver. In some instances, if troughs are orientedeast/west, then they are rotated as the seasons progress to aim at thesun. During the summer the trough is held somewhat horizontal, aimedmore or less straight up at the summer sun. During the winter the troughis held somewhat vertical, aimed toward the sun that is lower in the skyin the direction of the equator. In some instances, an east/west troughdoes not track the daily motion of the sun. Instead, when light comesfrom the east in the morning, it reflects off the trough and travelsfurther west until it hits the receiver. Similarly, in the evening, thelight hits the trough and travels further east down the trough until ithits the receiver.

SYNOPSIS

The invention may be implemented in numerous ways, including as aprocess, an article of manufacture, an apparatus, a system, and acomposition of matter. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. The Detailed Description provides an exposition of one ormore embodiments of the invention that enable improvements inperformance, efficiency, and utility of use in the field identifiedabove. The Detailed Description includes an Introduction to facilitatethe more rapid understanding of the remainder of the DetailedDescription. As is discussed in more detail in the Conclusions, theinvention encompasses all possible modifications and variations withinthe scope of the issued claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a perspective view of selected details of a portionof an embodiment of an enclosing greenhouse and an enclosed concentratedsolar energy system utilizing a parabolic trough with a unilateralextension.

FIG. 2 a illustrates a cross-section view of a bilaterally symmetrictrough with a symmetric portion and a unilateral extension collectivelyhaving one continuous shape.

FIG. 2 b illustrates a cross-section view of a bilaterally symmetrictrough with various styles of unilateral extensions.

FIG. 3 a illustrates a cross-section view of paths of selected incidentlight hitting a bilaterally symmetric trough with a unilateral extensionand reflecting onto a secondary reflector and a solar receiver.

FIG. 3 b illustrates a cross-section view of a solar receiver, a solarreceiver insulator, and an integrated secondary reflector, and alsoillustrates paths of selected light rays.

FIGS. 4 a and 4 b respectively illustrate selected details of anembodiment of a greenhouse enclosure with enclosed solar concentratorsutilizing a fixed unilateral extension and solar receivers in respectiveincident sunlight contexts: high angle (summer) and low angle (winter).

FIGS. 5 a and 5 b respectively illustrate selected details of anembodiment of a greenhouse enclosure with enclosed solar concentratorsutilizing a movable unilateral extension and solar receivers inrespective incident sunlight contexts: high angle (summer) and low angle(winter).

FIGS. 6 a and 6 b illustrate perspective views of selected details of anembodiment of suspension mechanisms enabled to suspend solar receiversfrom greenhouse superstructure and suspend solar concentrators withrespective focal points fixed on the respective solar receivers.

FIG. 7 illustrates a perspective view of selected details of anembodiment of a parabolic trough solar concentrator with a unilateralextension, a solar receiver, and a suspension mechanism that enable thesolar concentrator to rotate about the solar receiver.

FIGS. 8 a and 8 b illustrate views of selected details of an embodimentof a solar receiver, solar receiver insulation, and an integratedsecondary reflector, and further illustrate some paths of incident lightto the secondary reflector and the solar receiver.

FIGS. 9 a and 9 b illustrate respective shapes and focal points oftroughs of equal aperture, illustrating respectively a bilaterallysymmetric trough and a trough with a shortened focal length and aunilateral extension.

FIGS. 10 a and 10 b respectively illustrate percent of energy receivedat a solar receiver under equal conditions for each point in an apertureof a solar concentrator, respectively for a bilaterally symmetric troughand a trough with a shortened focal length and a unilateral extension.

FIGS. 11 a and 11 b respectively illustrate efficiency as measured byposition of a shade line in an aperture and by percent of shadingrespectively for a bilaterally symmetric trough and a trough with ashortened focal length and a unilateral extension.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures illustrating selecteddetails of the invention. The invention is described in connection withthe embodiments. The embodiments herein are understood to be merelyexemplary, the invention is expressly not limited to or by any or all ofthe embodiments herein, and the invention encompasses numerousalternatives, modifications, and equivalents. To avoid monotony in theexposition, a variety of word labels (including but not limited to:first, last, certain, various, further, other, particular, select, some,and notable) may be applied to separate sets of embodiments; as usedherein such labels are expressly not meant to convey quality, or anyform of preference or prejudice, but merely to conveniently distinguishamong the separate sets. The order of some operations of disclosedprocesses is alterable within the scope of the invention. Wherevermultiple embodiments serve to describe variations in process, method,and/or features, other embodiments are contemplated that in accordancewith a predetermined or a dynamically determined criterion performstatic and/or dynamic selection of one of a plurality of modes ofoperation corresponding respectively to a plurality of the multipleembodiments. Numerous specific details are set forth in the followingdescription to provide a thorough understanding of the invention. Thedetails are provided for the purpose of example and the invention may bepracticed according to the claims without some or all of the details.For the purpose of clarity, technical material that is known in thetechnical fields related to the invention has not been described indetail so that the invention is not unnecessarily obscured.

INTRODUCTION

This introduction is included only to facilitate the more rapidunderstanding of the Detailed Description; the invention is not limitedto the concepts presented in the introduction (including explicitexamples, if any), as the paragraphs of any introduction are necessarilyan abridged view of the entire subject and are not meant to be anexhaustive or restrictive description. For example, the introductionthat follows provides overview information limited by space andorganization to only certain embodiments. There are many otherembodiments, including those to which claims will ultimately be drawn,discussed throughout the balance of the specification.

In some circumstances, techniques described herein enable cost reductionof concentrated solar power systems. In various embodiments, collection(concentration and conversion of solar energy) is separated fromprotection. A protective transparent exoskeleton (such as a glasshouseor a greenhouse) surrounds and/or encloses collecting elements (oralternatively the collecting elements are placed in the exoskeleton),enabling the collecting elements (mirrors, lenses, etc) to be lessrobust than otherwise required. By separating collecting and protectingfunctions, and leveraging off-the-shelf technology (e.g. highlyengineered, cost effective, and proven greenhouse technology, such asglass growers greenhouse technology) for the protection function, insome circumstances a reduction in cost and complexity of a system (suchas mirrors/lenses, support structure, foundations, tracking mechanisms,etc.) is enabled with a relatively minimal impact on overallperformance. The glasshouse is relatively low to the ground with littlewind force bearing surfaces, and is designed to withstand wind andweather with a relatively minimal structural skeleton. Because theglasshouse reduces wind forces acting on the collector and receiverelements, the mirrors or lenses used for collection and concentrationinside the exoskeletal protection of the glasshouse are enabled to belightweight, in some embodiments, to a point of seeming flimsy, and thusare relatively less costly to construct, transport, support and aim, andhave little or no weatherization costs. Note that within thisdisclosure, the terms glasshouse and greenhouse are usedinterchangeably, and are not meant to necessarily imply any sort ofhorticultural activity.

The protected embodiment techniques enable reflectors built from lightermaterials with simpler and lighter frames since wind, weather, and UVlight are reduced inside a glasshouse enclosure. Foundation, suspension,and tracking mechanisms for receivers and concentrators are enabled tobe simpler, lighter, and less expensive.

Some embodiments of a concentrated solar system inside a glasshouse havean array of relatively large 2-D-freedomed, 1-D-solar-tracking parabolictroughs suspended from fixed roof locations.

A glasshouse, such as a commercial greenhouse, efficiently supports flatglass planes. Supporting framework of straight metal sections brace eachother and attach to the ground in multiple places. Some glasshousesdesigned to withstand the same weather conditions as an externalparabolic dish require less than half as much structural steel (lessthan 10 kg) per square meter of concentrator, compared to an externalparabolic dish. Total weight, including 4-5 mm glass, is less than 20 kgper square meter of concentrator, for the glasshouse.

According to various embodiments, concentrators are made entirely orpartially of thin-gauge aluminum foil, reflective film, or otherrelatively reflective and lightweight materials. Some of the materialshave higher reflectivity than glass mirrors. Concentrators, in someembodiments, are foam core combined with reflective material, enablingconcentrators weighing less than one kg per square meter. Lightweightconstruction, in some usage scenarios, reduces one or more of costsassociated with production, transportation, and installation ofconcentrators. Total weight for some enclosed concentrated solar energyembodiments (including exoskeleton and protected collector) is less than20 kg per square meter of concentrator.

The glasshouse structure is primarily fixed and immobile, and trackingsystems control and aim the less than one kg per square meterconcentrators inside the structure in an environment having relativelysmall wind forces.

In some embodiments, a commercial greenhouse is a suitable enclosure astaught by the techniques described herein. Growers have determined thatfor many types of plants, 1% less light reaching plants equals 1% lesscrop growth and hence profit. Greenhouse designs are optimized to reducecost, structural shading, glass reflective losses, and glasstransmission losses. In some usage scenarios, the structural shading,glass reflective losses, and glass transmission losses cause a majorityof lost sunlight. The Dutch Venlo design is relatively efficient atreducing the losses. Options available in commercial greenhouses includelow-shading structural design, anti-reflective glass coatings (to reducereflective losses), and low-iron glass (to reduce transmissive losses).

In some embodiments, sunlight losses due to a glasshouse enclosure areless than 20% at 33 degrees latitude without an anti-reflective coatedglass. In some embodiments using anti-reflective coated glass, lossesare 13%. In some embodiments, techniques described herein improvesalvage value of a system in one or more of obsolescence, abandonment,and destruction and/or damage due to storm, ice, corrosion, andearthquake events.

A commercial greenhouse has multiple uses and has, in some embodimentsand/or usage scenarios, a ready sale market for a greenhouse sold inplace or for relocation. In some embodiments, a greenhouse enclosure ofa concentrated solar energy system is a significant portion of thesystem cost. Resale value of the greenhouse, in some usage scenarios,lowers overall risk of a solar energy project and/or reduces financingcosts.

In some embodiments, long, continuous, fixed receivers are advantagedover other systems to avoid complex and expensive mechanisms such asmoving fluid joints or hoses to connect the thermal medium system. Insome embodiments and/or usage scenarios, selected components (such asreceivers or pipes) that are fixed during a tracking mode of operationare permitted to move or are moved due to expansion and contraction ofmaterials or for cleaning during a maintenance mode of operation.

Thermal conduction and convection increase with wind speed, thusreducing efficiency of solar thermal receivers. In some non-enclosedconcentrated system approaches, solar energy receivers are protectedfrom environmental effects including heat loss and physical damage by anat least partially transparent protective enclosure for each receiver.In some enclosed embodiments, thermal energy receivers are enabled tominimize heat loss without using an enclosure for each receiver.

In some embodiments, a greenhouse enclosure is a fixed cost and asignificant portion of overall system cost. Thus it is beneficial tohave as much of the light that comes into the greenhouse hit a mirrorand reflect to a receiver as feasible during all seasons and all timesof day. A technique of tightly packing troughs, covering as much groundas feasible, is beneficial when implementing a CSP system inside agreenhouse. In addition to more effectively using the space enclosed bythe greenhouse, such a technique also more effectively uses land area toproduce solar heat and power. Such a technique is enabled in part byconcentrators inside a greenhouse that are relatively inexpensive sincethe concentrators are not subject to significant environmental insultssuch as wind, rain, and dust.

In some embodiments, such as some embodiments operating at hightemperatures (e.g. above 300 degrees Celsius), heat loss from receiversrepresents a significant overall system cost. Thus, it is desirable tominimize receiver size to minimize surface area of the receiver and thusto minimize heat losses from the receiver. In some embodiments, ashorter focal length parabolic trough with a smaller aperture enablesuse of a smaller receiver, since smaller lengths and angles reduceeffects of manufacturing tolerances and of arc size of the sun.

One technique to tightly pack troughs to capture more incident lightwithin an enclosure, is to use more troughs and place them closertogether to fill up the enclosed space. This results in more totalreceiver length (since there are more troughs) and so more total thermalloss and pumping cost. Such a system gathers more light in summer whenthe sun is overhead and the troughs are in a horizontal position notshading each other, but collects no more light in winter, due toshading, than a system with fewer troughs spaced far apart. Anothertechnique is to use longer focal length troughs with a wider aperture,again placed closer together. This preserves total receiver length butuses larger receiver pipe to capture light from a longer focal lengthmirrors and the larger aperture, thus increasing thermal loss or imposestighter tolerance on a concentrator to maintain focus, thus increasingcost and complexity. Some of the embodiments described herein, whendeployed in an east/west orientation and tracking seasonal motion of thesun, use an asymmetric trough design wherein one side of a short focallength trough is extended further than the other side in an extensionarea of the trough. In the winter, when the troughs are angled up toface the winter sun, the extension areas are in shade and gather noenergy, but base portions of the short focal length troughs are in sun,and intercept almost all available light. In the summer, when thetroughs are more horizontal to face the high in the sky sun, the shortfocal length center of the troughs enable capture of much of the lightand reflect that light to a small diameter receiver. The extension isnow illuminated as well, and captures the rest of the light that wouldotherwise be lost without the extension.

The extension section of the trough has a longer distance to thereceiver and so will not naturally focus as well. In the a relativelysimple design, efficiency of the extension is allowed to be lower thanthat of a remainder of a trough (such as 70%) since the extension isused only for a fraction of the year and for a fraction of incidentlight. Alternately, a small secondary reflector is used to capture lightreflected from the extension that misses the receiver, and reflect thatlight back to the receiver. A secondary reflector about two times thediameter of the receiver enables capture of almost all the light fromthe extension. A secondary reflector enables a receiver of a same sizeas without the extension and without increasing thermal losses. In someembodiments, a partial insulator and convection shield are integratedwith the secondary reflector to reduce the thermal losses from thereceiver.

In some embodiments of an asymmetric trough, e.g. having a largeraperture than a base symmetric portion of the trough, greenhouse heightis increased to make room for an extension to clear the ground when thetrough is vertical, thus increasing the cost, edge effect shading, anddesign and/or manufacturing complexity of the greenhouse. A movablehinge connecting the trough extension to the base portion of the troughenables a reduction of the increase in the greenhouse height. During thewinter, the trough is raised to face the sun and the extension is movedon its hinge to remain essentially horizontal to the ground. Thus, theheight of the trough with a hinged extension during the winter islimited by the base portion of the trough and not increased by theextension. During the summer, the trough is held more nearly horizontaland the extension is returned to be a continuous extension of a(parabolic shape, e.g.) of the asymmetric trough.

Some embodiments orient troughs on a north/south axis and rotate thetroughs to track daily motion of the sun. In such embodiments, a movablyhinged extension on each side of the trough (a “top” extension and a“bottom” extension) are optionally used. During morning, a trough isheld facing east toward the sun. The top extension is flipped behind thetrough to reduce or eliminate shading of a longitudinally adjacenttrough, while the bottom extension is held horizontal to the ground toprevent hitting the ground. Only the base portion of the trough isilluminated. At noon, the trough is horizontal to the ground, pointingat the sun high in the sky. The two extensions are in respectiveoperating positions, providing an extended trough of a larger effectiveaperture. In evening, the trough is held vertical facing west, with theextensions held similarly to the morning. Thus at all times of day, mostincident light (such as within a greenhouse) is captured by aconcentrator.

Integration of Receiver and Greenhouse Structure

In some embodiments, a receiver and concentrator are suspended fromsuperstructure of an enclosing greenhouse, enabling use of substantialsupport infrastructure of structure of the greenhouse. Lightweightreceivers and troughs, hung from the greenhouse (e.g. roof structure,trusses, and/or end posts), are held in place and aimed with relativelysmall members that exert force mostly in tension, thus avoiding use ofrelatively larger members compared to structures held in place and movedwith members in compression and subject to bending. The receiver issuspended at a fixed position relative to the greenhouse and theconcentrator is suspended with its focal line held on the receiver butable to rotate around the receiver to track the daily and/or seasonalmotion of the sun.

In some embodiments, a receiver pipe expands (such as by about ½percent) when heated by thermal transport fluid transported in thereceiver pipe. In some usage scenarios, a 500 foot pipe expands abouttwo feet. In some embodiments, the receiver pipe is held in a fixedposition at a “fixed” end of the pipe at one end of the greenhouse, andenabled, by hangers, to expand and contract along its length toward theother “non-fixed” end of the pipe. The hangers suspend the receiver pipefrom superstructure of the greenhouse, and are designed so that when thereceiver pipe is hot and at maximum extension (while operating), eachhanger is vertical and the receiver pipe is horizontal. When thereceiver pipe is cool and contracts (while not operating), each hangerbottom is pulled slightly toward the fixed end of the receiver pipe andthe receiver pipe is pulled slightly higher at the non-fixed end. Whenthe receiver pipe is cool, each successive hanger is slight pulled insuch that the hanger at the non-fixed end of the receiver pipe is pulledin (e.g. as much as two feet). For example, with approximately six foothangers, the (cool) receiver pipe rises less than a foot relative to theother end of the receiver pipe. The concentrators are at a fixeddistance and rise fall with the receiver pipe, thus preserving focus.

Design of Hanger, Rotating Joint and Bearing

In some embodiments, a hanger with a rotating joint is held in placesuspended from roof superstructure of a greenhouse. A receiver tube isrigidly connected to the hanger, thus supporting the receiver tube. Therotating joint is connected to the hanger with a bearing enabling thejoint to rotate around the receiver tube. A trough is suspended from therotating joint. All the weight of the joint and the trough is carried bythe rotating joint, through a bearing and to the hanger and then up tothe roof superstructure. The rotating joint is enabled to rotate forsmall adjustments during the day, through about ½ turn from winter tosummer, and another ½ turn back from summer to winter. In some usagescenarios, during an entire lifetime of the joint, it rotates theequivalent of no more than 100 revolutions and never needs to rotatemore than about 1 rpm. The bearing and the rotating joint are designedto avoid shading the receiver tube and to withstand high temperatures(e.g. hundreds of degrees C.) since the bearing and the joint arenecessarily in close thermal proximity to a high temperature thermalmedium and the receiver tube.

Concentrated Solar Energy System

Industrial scale concentrated solar power systems, in some embodiments,cover multiple acres of land, with large-scale systems practical in thehundreds of acres. FIG. 1 illustrates a perspective view of selecteddetails of an embodiment of an enclosing greenhouse and an enclosedconcentrated solar energy system for a small portion of a system.Greenhouse 25 has low internal shading and low cost. According tovarious embodiments, the greenhouses are less than an acre to hundredsof acres in size. Suitable commercial greenhouses are available withshort lead times from various vendors. Additionally, in some usagescenarios, there is a market for used greenhouses, enabling relativelyeasier financing of large-scale concentrated solar energy projects, suchas described herein. Elements of the greenhouse include a roof systemwith multiple peaks and gutters. The roof system is enabled to drainwater efficiently from the roof structure, to keep incident angles ofsunlight relatively close to directly normal to transparent roofmaterial to reduce reflection, and to keep roof support members incompression. Sidewalls of the greenhouse further enclose interior spaceof the greenhouse and have transparent covering where sunlight isincident thereon and are optionally of any appropriate material wherelittle sunlight is incident. The greenhouse structure is enabled to keepmost wind, rain, and other environmental elements from the interior, andis optionally not entirely weather tight. An optional fan drivenoverpressure filtration system (not illustrated) optionally providesrelatively clean pressurized air to the interior to further inhibitinfiltration of dust and other elements to the interior. The lack (orreduction) of dust reduces or eliminates a need to clean concentrators(such as concentrators 27 and 28), reducing operating costs and enablinguse of less robust and less scratch resistant reflective concentratormaterials, in some usage scenarios and/or embodiments. In some operatingconditions, concentrators shade each other as illustrated by frontconcentrator 27 in front of and shading concentrator rear 28. In someembodiments, concentrator troughs are much greater in length than width,with an aspect ratio of between 10-1 and 33-1 rather than theapproximately 3-1 aspect ratio illustrated. In some embodiments, manytroughs are enclosed in a single greenhouse with one front trough 27 andall the rest rear troughs such as 28. In some embodiments, the troughsare aligned east/west, with troughs facing the equator as illustrated,and track seasonal movement of the sun. In some embodiments, the troughsare aligned north/south (not illustrated).

In some embodiments, all elements of the concentrated solar energysystem are located within a protected interior of a greenhouse.Greenhouse transparent cover material 53 is glass or any materialgenerally transparent to sunlight. The transparent cover optionallyincludes an ultra violet (UV) blocking coating or film to enable use ofplastics inside the greenhouse (such as reflective plastic mirror filmsfor the concentrator surfaces) that would otherwise break downrelatively rapidly. In some embodiments, solar receivers, such asimplemented in part by receiver pipe 12, are held at somewhat fixedpositions during sunlight collecting operation to reduce a need forflexible joints carrying a thermal medium. The solar receivers areinterconnected through a series of thermally insulated pipes (such aspipe 8). In a concentrated solar thermal (CST) system, heated thermalmedium is a primary output of the system and is fed to an industrialprocess. In a direct electric system, such as a concentrated photovoltaic (CPV) system, a thermal medium optionally provides cooling to PVcells or other aspects of the receiver. Excess heat in the thermalmedium of a CPV system is optionally used in an industrial process.Measurement and control wires, power for motors, and various cabling isrouted with the thermal medium pipes, in some CST and CPV embodiments.

In FIG. 1, line-focus solar receivers are illustrated and are suspendedfrom receiver pipes 12 that are in turn suspended from the roof of theenclosing greenhouse. Line-focus solar concentrators are suspended fromassociated solar receivers so that the focal point of the concentratoris held relatively fixed on the receiver while the concentrator bodyremains free to rotate around the receiver (in one degree of freedom) totrack daily and seasonal motions of the sun. The arrangement ofrelatively fixed receivers and concentrators that rotate around thereceivers to track the sun is enabled, at least in part, by low weightof the concentrators and absence of wind forces on the concentrators.

Some trough solar concentrators (such as solar concentrator 27), have asymmetric primary portion, e.g. built of symmetric facets (such as basetrough section 6), and a secondary section, e.g. built of one or moreextension facets (such as extended trough section 7). When held in avertical position to aim at winter sun, the extension section is atbottom 26 of trough.

Shape of Trough and Definitions of Terms and Formula

FIG. 2 a illustrates a shape of a parabolic trough with an extension,such as an embodiment of an asymmetric (parabolic) trough. The shape ofthe parabolic trough is defined by the formula y²=4fx. With examplevalues described following, an example parabola is defined by theformula y²=5.8x, where −2.29<x<4. A primary symmetric portion includestwo symmetric base trough sections 6 a and 6 b referred to andillustrated collectively as base trough section 6, and also sometimesreferred to as (symmetric) base portion (of the trough). A secondaryextended portion includes extended trough section 7, and is, in someembodiments, a unilateral extension of the parabolic shape. Bottom oftrough 26 is the edge of the trough that is closest to the ground whenthe trough is held vertical to face the sun low in the sky. Top oftrough 30 is the edge of the trough that is furthest from the groundwhen the trough is held vertical. In some embodiments, bottom of trough26 is the edge of extended trough section 7, and is further from theground when the trough is horizontal, pointed at the sun high in the sky(as illustrated in FIG. 2 a, given an orientation of the trough suchthat construction line 34 is essentially horizontal to the ground).Trough focal length, illustrated by construction line 32 (e.g. having avalue of 1.45 meters), is represented by the symbol f. A symmetrictrough has an aperture (referred to as a base aperture in a trough withan extension), defined by a construction line between its two edges,such as illustrated by construction line 34 across the symmetric portionand ending at construction line 44, denoting intersection of the primaryand the secondary portions of the trough. Construction line 35represents a half-portion of construction line 34 (e.g. having a valueof 2.29 meters). Construction line 33 indicates an extended aperture(e.g. having a value of 6.29 meters) of the asymmetric trough (referredto simply as the aperture where clear from context), including basetrough section 6 and extended trough section 7. In some embodiments,extended trough section 7 is optionally movably connected to base troughsection 6, is optionally enabled to change shape and/or is optionallyenabled to change focus at an intersection defined by construction line44. Construction line 48 defines an axis of symmetry of the symmetricbase portion of the trough and runs from the intersection of base troughsections 6 a and 6 b through focal point 36. Angles 37 a and 37 b arebase rim angles (sometimes referred to as the base rim angle forclarity) of the symmetric portion of the trough. Angle 38 is theextended rim angle of the extended portion.

FIG. 2 b illustrates various techniques for a secondary extension. Invarious embodiments, extension 45 is a continuation of a parabolic shapeof a primary portion, shares a focal point with the primary portion, andis connected at an intersection defined by construction line 44 eitherfixedly or by a movable hinge. In various embodiments, extension 46 isan alternate shape, has a focal point that is distinct from the primaryportion, and is connected at an intersection defined by constructionline 44 either fixedly or by a movable hinge. In various embodiments,extension 47 is a flat shape, has a focal point that is distinct fromthe primary portion, and is connected at an intersection defined byconstruction line 44 either fixedly or by a movable hinge.

Incident Sunlight Transmission

In some embodiments, solar concentrators as large as will fit insidelarge standard commercial greenhouses (e.g. roughly in a six meteraperture range), are used. Each solar concentrator is associated with adrive mechanism and a solar receiver, thus increasing concentrator size(correspondingly reducing how many are used in a particular area), andreducing the number of the drive mechanisms and/or the solar receivers,reducing cost overall. In various embodiments, one or more concentratorsshare a same drive mechanism.

Irradiance characterizes power of incident electromagnetic radiation(such as sunlight) at a surface, per unit area. Some sunlight lossescaused by the greenhouse enclosure glass and structural shading aredetermined by comparing direct normal sunlight received inside thegreenhouse enclosure (interior) with unimpeded direct normal sunlightreceived outside the greenhouse enclosure (exterior). In absolute terms,irradiance loss is highest at midday; considered relatively, theirradiance loss is highest in mornings and evenings. FIGS. 3A and 3Billustrate selected details of an embodiment of a solar concentrator andsolar receiver.

FIG. 3 a illustrates paths of incident radiation 41 that has comethrough the greenhouse enclosure and is reflected off base troughsection 6 and extended trough section 7. Reflected light 42 from basetrough section 6 is focused onto receiver pipe 12. In some embodiments,receiver pipe 12 diameter is sized so that most (such as 95% or more) ofreflected light from base trough section 6 hits receiver pipe 12, takinginto account angle of incident radiation (due to the extent of the sun)and manufacturing tolerances. In some embodiments, insulating jacket 20is used to reduce heat loss from receiver pipe 12. In some embodiments,reflected light 43, 49, and 50 from extended trough section 7 is lesswell focused than reflected light 42 from the base trough sections, suchas with 95% of reflected light subtending twice the area at the focalpoint as light reflected from the base trough sections due to the longerdistances from extended trough section 7 to receiver pipe 12.

FIG. 3 b illustrates in more detail a design of receiver pipe 12,insulating jacket 20, and integrated secondary receiver 21. In someembodiments, secondary reflector 21 is implemented with a reflectivecoating applied to a portion of insulating jacket 20. In someembodiments, secondary reflector 21 is used to extended capture area ofincident light from a secondary portion without increasing size ofreceiver pipe 12. Secondary reflector 21 reflects light incident fromextended trough section 7 onto receiver pipe 12. In some embodiments,secondary reflector 21 is approximately equal in cross section size asreceiver pipe 12 and is positioned above receiver pipe 12 as seen fromextended trough section 7. In some embodiments, extended trough section7 is designed so that its focal point is directly between receiver pipe12 and secondary reflector 21 so that half the light reflected fromextended trough section 7 directly hits receiver pipe 12 and half thelight hits secondary reflector 21 and is then reflected to receiver pipe12. Incident light 49 to top of secondary reflector 21 and 43 to bottomof secondary reflector 21 reflect at various angles depending on theangle of incidence in paths such as paths 51 to receiver pipe 12.

Selected Greenhouse Details

In some embodiments, a greenhouse includes roof peaks (such as roof peak54 of FIG. 4 a) that in combination with included roof gutters (such asroof gutter 55 a) are enabled to drain water over a large space and toangle transparent roof material relatively close to direct normal toincident sunlight in summer and in winter. A roof system with peaks andgutters is referred to as a “ridge and furrow” style roof, in some usagescenarios, and in some embodiments, is a form of a “gutter-connected”roof system. The greenhouse includes support columns (such as supportcolumn 29). Some of the support columns are arranged around theperiphery of the greenhouse and others of the support columns arearranged within the greenhouse. In some embodiments, the greenhouseincludes support columns at every roof gutter (such as support columns57 a, and 57 b located at roof gutters 55 a, and 55 b, respectively, ofFIG. 4A). In alternate embodiments, every other support column isomitted (such as support column 57 a being omitted) and trusses (such astruss 1) are horizontal lattice girders. Roof gutters without supportcolumns are floating gutters (e.g. roof gutter 55 a). Some of theembodiments that omit every other support column are implemented with aVenlo style greenhouse. Various embodiments suspend pipes 8 and receiverpipes 12 from trusses 1 or horizontal lattice girders. Variousembodiments suspend pipes from trusses or horizontal lattice girders andfurther suspend receivers from pipes.

Selected Mounting and Control Mechanism Details

FIGS. 4 a and 4 b illustrate a parabolic trough with a fixed unilateralextension including extended trough section 7 enclosed in greenhouse 25held in a horizontal (summer) position and a vertical (winter) positionrespectively. A rotating suspension mechanism and a receiver pipe areoutlined by construction line 52 and illustrated in more detail in FIGS.6 a and 6 b. Suspension hanger 16 is suspended from greenhouse truss 1by suspension members 2. Base trough section 6 is suspended fromsuspension hanger 16 by fixed base trough suspension members 4 and fixedextension suspension member 5 f that hold the trough at a fixed distancefrom the receiver pipe, with a focal line of the trough on (orconcentric with) the receiver pipe. Suspension members 4 are connectedto base trough section 6 and extended trough section 7 with troughsection connectors 15. Insulated pipe 8 connects the trough receiverpipe to a next trough receiver pipe to complete a thermal fluid circuit.

Top of trough 30 and bottom of trough 26 in a maximum vertical winterposition determine a height requirement for a greenhouse such thatbottom of trough 26 does not hit floor of greenhouse 39 and top oftrough 30 does not interfere with truss 1.

In some embodiments, counterweight 14 is used to balance a trough sothat its resting position is at least as vertical as the most verticalposition used for solar energy collecting operation, enablingpositioning the trough through all its operating positions bypositioning member 9 that is shortened or lengthened as required bywinch 11. In some embodiments, all support and positioning members 2, 4,5 f and 9 are designed to operate only in tension. In some embodiments,some or all of support and positioning members 2, 4, 5 f and 9 areoptionally flexible members such as wire, monofilament, or rigid memberswith low strength under compression and torsion. In some embodiments,gear ratio and torque requirements of winch 11 are minimized byconnecting positioning member 9 far from an axis of rotation of thetrough. In some embodiments, positioning errors due to gear lash and dueto gear and other member manufacturing tolerances, are minimized becausepositioning member 9 is always held in tension when the trough isoperational, and gravity is sufficient as a counterforce in positioningthe trough since wind is minimized inside enclosure 25.

Selected Details of a Movable Hinged Extension

FIGS. 5 a and 5 b illustrate, respectively, a trough with a movableextension, otherwise similar to, respectively, the trough with the fixedextension illustrated in FIGS. 4 a and 4 b. In FIGS. 5 a and 5 b,section connector 15, at the intersection of base trough sections 6 andextended trough section 7, is conceptually replaced with hinged sectionconnector 13. Fixed extension suspension member 5 f of FIGS. 4 a and 4b, is conceptually replaced by movable extension suspension member 5 mof FIGS. 5 a and 5 b. In some embodiments, movable extension suspensionmember 5 m is a rigid bar fixedly connected to the outside edge ofextended trough section 7 and coupled (e.g. via direct mechanicalconnection or via one or more intermediate mechanical members) to hanger16 to enable sliding. Extension stop member 10 is fixedly connected totruss 1 and connected to extended trough section 7 to enable sliding. Ina summer position illustrated in FIG. 5 a (and in any position where theextension is operational) movable extension suspension member 5 m slidesto a stop at hanger 16, and holds extended trough section 7 in anoperating position as an extension of base trough section 6, whileextension stop member 10 slides free and does not influence the positionof extended trough section 7. In a winter position illustrated in FIG. 5b (and in any position where the extension is stowed andnon-operational), movable extension suspension member 5 m slides freeand does not influence the position of extended trough section 7, whileextension stop member 10 slides to a stop at the edge of section 7, andholds extended trough section 7 in its non-operation (stowed) positionabove floor 39 of greenhouse 25. Construction line 40 illustrates thelowest point touched by any part of the trough mechanism with themovable extension and so the distance between construction line 40 andgreenhouse floor 39 represents a reduction in greenhouse height enabledby the movable hinged extension compared to an extension that is notmovable (e.g. fixed).

In some embodiments with a movable extension section, counterweight 14is sized so that the center of gravity of a trough system provides acountervailing force against positioning member 9, when movableextension support member 5 m is engaged, as well as when extension stopmember 10 is engaged, and is sufficient to counter any forces that insome usage scenarios would otherwise raise bottom of trough 26.

In some embodiments, rigid sliding movable extension support member 5 mis implemented with a flexible member (such as wire or monofilament) ofa length determined to hold extended trough section 7 in properoperating position when under tension (as held by gravity) and that isslack and exerts no influence on position of extended trough section 7when extended trough section 7 is held in a stowed position by extensionstop member 10.

FIGS. 6 a and 6 b illustrate details of an area outlined on FIGS. 4 a, 4b, 5 a, and 5 b by construction line 52. FIG. 6 a is a perspective viewfrom the side of hanger 16 that rotating joint 3 is mounted on, whileFIG. 6 b is a perspective view from the opposite side. A connectingfastener (not illustrated) is used at location 31 to connect hangersuspension members 2 and trough suspension members 4 to hanger 16 androtating joint 3 respectively. Receiver pipe 12 is suspended and fixedlyconnected to hanger 16. Movable extension suspension member 5 m isconnected to rotating joint 3 through sliding connector 17 (used formovable hinged extension embodiments). In FIG. 6 a, movable extensionsupport member 5 m is in the state where extension support member stop18 is not engaged with sliding connector 17, and so movable extensionsupport member 5 m is not influencing the position of the extensiontrough section. This is a non-operational position of the extensiontrough section (e.g. during winter or maintenance). In FIG. 6 b, movableextension support member 5 m is in the state where extension supportmember stop 18 is not engaged with sliding connector 17 and so movableextension support member 5 m is holding the position of extension troughsection. This an operational position of the extension trough section(e.g. during summer). In an embodiment with a fixed extension, movablesupport member 5 m is held fixed with its stop 18 engaged. In someembodiments, rotating joint 3 is connected to hanger 16 with a bearing(not illustrated in detail), enabling rotating joint 3 to rotate aroundhanger 16.

FIG. 7 illustrates certain details of a parabolic trough with anextension, a receiver pipe, and an associated suspension mechanisms in acontext free of other details to make certain details easier tounderstand. Extension suspension member 5 is representative ofembodiments with fixed extension suspension member 5 f and movableextension suspension member 5 m, as appropriate.

FIGS. 8 a and 8 b illustrate certain details of receiver pipe 12,insulating jacket 20, secondary reflector 21, hanger 16, and variouslight paths to make certain details easier to understand. Incident lightrays (22 i, 23 i, and 24 i) are reflected off of secondary reflector 21as respective reflected light rays (22 r, 23 r, and 24 r).

In some embodiments, construction and suspension of a trough isaccomplished by pinning together various elements, including suspensionmembers 2, 4, and 5, hanger 16, base trough section 6 and extendedtrough section 7. Each segment of the concentrator is made frompre-formed mirror surfaces having sufficient internal structure to holdshape and curvature without use of other elements, while under the forceof gravity and small forces imposed by suspension and positioning. Theconcentrators are enabled for inside use, protected by a greenhouse, andso are not strong enough to withstand wind force or environmentalelements such as rain and dust. Suspension members are either lightrigid members or wires. In either case, the suspension members connectto the concentrator surface, joint, hanger, or roof superstructure withpins that are readily insertable for assembly and readily removable forservice.

Graphs Comparing Performance of Standard Trough to Trough with Extension

FIGS. 9 a and 9 b are graphs of a focal point and a shape of a mirror ofa symmetric trough without an extension, and an asymmetric trough withan extension, respectively. Both troughs have an aperture of 5.8 meters.FIGS. 10 a and 10 b are, respectively, plots of percent of energyreceived at a receiver pipe for each trough. For the symmetric trough(with a relatively long focal length as illustrated in FIG. 10 a), areceiver pipe of 50 mm diameter is used to achieve an intercept factorabove 80% across the surface of the mirror while minimizing receiverpipe diameter. In FIG. 10 b, a smaller receiver pipe of 40 mm is used,because the relatively shorter focal length of the asymmetric troughenables a higher average intercept factor with a smaller, and so moreefficient, receiver pipe. The mirror of the extension section (termedthe secondary in the plot) falls below an 80% intercept factor at itsoutside edge, but this edge is only used in summer, and the overallintercept factor of the asymmetric trough remains better than that ofthe symmetric trough. In FIG. 11 a, performances of the symmetric andthe asymmetric troughs are plotted together as a shade line progressesacross the mirror. The asymmetric trough starts producing useful energysooner as the shade line moves off the mirror, and in all positions ofthe shade line, outperforms the symmetric trough. FIG. 11 b is a plot ofthe same data as a function of percent of the mirror surface that isshaded, and again demonstrates that the asymmetric trough outperformsthe symmetric trough.

Selected Embodiment Details

In various embodiments and/or usage scenarios, the illustratedembodiments are related to each other. For example, in some embodiments,movable extension suspension member 5 m of FIGS. 5 a, 5 b, 6 a, and 6 b,is appropriate for use in various embodiments as an implementation offixed extension suspension member 5 f of FIGS. 4 a and 4 b.

While the forgoing embodiments are described as having roof systems withpeaks and gutters, other embodiments use alternate roof systems, such aspeaked, arched, mansard, and Quonset-style roof systems, as well asvariations and combinations thereof. In various embodiments, a partiallytransparent protective enclosure (such as a glasshouse or a greenhouse)uses glass to provide the transparency, and other embodiments usealternative transparent materials such as plastic, polyethylene,fiberglass-reinforced plastic, acrylic, polycarbonate, or any othermaterial having suitable transparency to sunlight and sufficientstrength (in combination with a supporting framework) to provideenvironmental protection.

CONCLUSION

Certain choices have been made in the description merely for conveniencein preparing the text and drawings and unless there is an indication tothe contrary the choices should not be construed per se as conveyingadditional information regarding structure or operation of theembodiments described. Examples of the choices include: the particularorganization or assignment of the designations used for the figurenumbering and the particular organization or assignment of the elementidentifiers (the callouts or numerical designators, e.g.) used toidentify and reference the features and elements of the embodiments.

The words “includes” or “including” are specifically intended to beconstrued as abstractions describing logical sets of open-ended scopeand are not meant to convey physical containment unless explicitlyfollowed by the word “within.”

Although the foregoing embodiments have been described in some detailfor purposes of clarity of description and understanding, the inventionis not limited to the details provided. There are many embodiments ofthe invention. The disclosed embodiments are exemplary and notrestrictive.

It will be understood that many variations in construction, arrangement,and use are possible, consistent with the description, and are withinthe scope of the claims of the issued patent. The names given toelements are merely exemplary, and should not be construed as limitingthe concepts described. Also, unless specifically stated to thecontrary, value ranges specified, maximum and minimum values used, orother particular specifications, are merely those of the describedembodiments, are expected to track improvements and changes inimplementation technology, and should not be construed as limitations.

Functionally equivalent techniques known in the art are employableinstead of those described to implement various components, sub-systems,operations, functions, or portions thereof.

The embodiments have been described with detail and environmentalcontext well beyond that required for a minimal implementation of manyaspects of the embodiments described. Those of ordinary skill in the artwill recognize that some embodiments omit disclosed components orfeatures without altering the basic cooperation among the remainingelements. It is thus understood that much of the details disclosed arenot required to implement various aspects of the embodiments described.To the extent that the remaining elements are distinguishable from theprior art, components and features that are omitted are not limiting onthe concepts described herein.

All such variations in design are insubstantial changes over theteachings conveyed by the described embodiments. It is also understoodthat the embodiments described herein have broad applicability to otherapplications, and are not limited to the particular application orindustry of the described embodiments. The invention is thus to beconstrued as including all possible modifications and variationsencompassed within the scope of the claims of the issued patent.

1-113. (canceled)
 114. A method for collecting solar energy, comprising:rotating a line focus concentrator about a receiver pipe inside aninterior region of a structure that is at least partially transparent tosolar radiation, wherein rotating the line focus concentrator isperformed using a drive mechanism attached to a structural member of thestructure, and wherein the line focus concentrator is suspended betweenground and the structural member of the structure; at least in somepositions of the line focus concentrator, counterbalancing a weight ofthe line focus concentrator with a counterweight attached to the linefocus concentrator; focusing the solar energy reflected from the linefocus concentrator on the receiver pipe; and flowing a thermal transportfluid through the receiver pipe.
 115. The method of claim 114 whereinthe line-focus concentrator comprises a longitudinal, bilaterallysymmetric primary portion and a secondary portion comprising aunilateral extension coupled to the primary portion at a coupling point.116. The method of claim 115, further comprising pivoting the secondaryportion about the coupling point.
 117. The method of claim 114, furthercomprising controlling a rotational position of the line focusconcentrator at least in part via closed-loop feedback.
 118. The methodof claim 114 wherein rotating the line focus concentrator about thereceiver pipe is performed at least partially in accordance withseasonal changes in declination of the sun.
 119. The method of claim 114wherein rotating the line focus concentrator about the receiver pipe isperformed at least partially in accordance with a predefined solartracking strategy.
 120. The method of claim 114 wherein the line focusconcentrator comprises a thin-gauge aluminum foil.
 121. The method ofclaim 114 wherein the line focus concentrator comprises a foam core.122. A method for collecting solar energy comprising: rotating a firstline focus concentrator about a first receiver pipe portion; rotating asecond line focus concentrator about a second receiver pipe portion,each line focus concentrator having: a longitudinal, bilaterallysymmetric primary portion having an at least approximately paraboliccurvature, and a secondary portion comprising a unilateral extension ofthe primary portion, wherein the unilateral extension continues thecurvature of the primary portion and shares with the primary portion acommon focal line; and shading the secondary portion of the secondline-focus concentrator with the primary portion of the first line-focusconcentrator.
 123. The method of claim 122 wherein the first and thesecond line focus concentrators are housed in an enclosure that is atleast partially transparent to solar radiation.
 124. The method of claim122, further comprising: rotating a secondary reflector about the firstreceiver pipe portion to direct solar energy from the first line focusconcentrator to the first receiver pipe portion.
 125. A method forcollecting solar energy, comprising: rotating a line focus concentratorabout a receiver pipe inside an interior region of a structure that isat least partially transparent to solar radiation, wherein— the linefocus concentrator is suspended between ground and a structural memberof the structure, and rotating includes rotating via flexible wirescoupled to a drive mechanism that is attached to the structural member,focusing the solar energy reflected from the line focus concentrator onthe receiver pipe; and flowing a thermal transport fluid through thereceiver pipe.
 126. The method of claim 125 wherein the structuralmember includes a truss, wherein an extension stop member is connectedto the truss, and wherein rotating the line focus concentrator includessliding the unilateral extension of the line focus concentrator alongthe extension stop member.
 127. The method of claim 125 wherein the linefocus concentrator comprises a thin-gauge aluminum foil.
 128. The methodof claim 125 wherein the line focus concentrator comprises a foam core.129. The method of claim 125 wherein the line focus concentrator weighsless than 20 kg per square meter.
 130. The method of claim 125 whereinthe line-focus concentrator comprises a longitudinal, bilaterallysymmetric primary portion and a secondary portion comprising aunilateral extension coupled to the primary portion at a coupling point.131. The method of claim 130, further comprising pivoting the secondaryportion about the coupling point.